U.S. patent number 4,447,521 [Application Number 06/436,266] was granted by the patent office on 1984-05-08 for fixing of tetra(hydrocarbyl)borate salt imaging systems.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Steven M. Aasen, Rex J. Dalzell, Brian N. Holmes, George V. D. Tiers.
United States Patent |
4,447,521 |
Tiers , et al. |
May 8, 1984 |
**Please see images for:
( Certificate of Correction ) ** |
Fixing of tetra(hydrocarbyl)borate salt imaging systems
Abstract
Imaging systems comprising a tetra(hydrocarbyl)borate and a
bleachable dye may be rendered desensitizable by the inclusion of a
second bleachable dye which absorbs radiation in a different
portion of the electromagnetic spectrum than the first bleachable
dye.
Inventors: |
Tiers; George V. D. (St. Paul,
MN), Aasen; Steven M. (Lakeland, MN), Dalzell; Rex J.
(Sommerset, WI), Holmes; Brian N. (Oakdale, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
23731779 |
Appl.
No.: |
06/436,266 |
Filed: |
October 25, 1982 |
Current U.S.
Class: |
430/337;
430/339 |
Current CPC
Class: |
G03C
1/735 (20130101); G03C 7/02 (20130101) |
Current International
Class: |
G03C
1/73 (20060101); G03C 1/735 (20060101); G03C
7/02 (20060101); G03C 001/52 () |
Field of
Search: |
;430/339,337 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1370058 |
|
Oct 1974 |
|
GB |
|
1370059 |
|
Oct 1974 |
|
GB |
|
1370060 |
|
Oct 1974 |
|
GB |
|
1386269 |
|
Mar 1975 |
|
GB |
|
Primary Examiner: Louie, Jr.; Won H.
Attorney, Agent or Firm: Sell; Donald M. Smith; James A.
Litman; Mark A.
Claims
We claim:
1. A desensitizable and imageable article having at least one layer
comprising a tetra(hydrocarbyl)borate, a first bleachable dye, and
a second bleachable dye present in a molar ratio of at least
0.8/1.0 with respect to said borate and said first bleachable dye
providing an optical density to said sheet, and having a spectral
absorption curve different from the said second bleachable dye
wherein said second bleachable dye is a substantially non-visible
dye absorbing in the infrared or ultraviolet regions of the
spectrum.
2. The article of claim 1 wherein said second bleachable dye
provides a visible optical density of less than 0.2.
3. The article of claim 1 wherein said tetra(hydrocarbyl)borate is
a tetra(aliphatic)borate.
4. The article of claim 3 wherein said tetra(aliphatic)borate is a
tetra(alkyl)borate.
5. The article of claim 1 wherein said non-visible dye absorbs
strongly in the ultraviolet region of the spectrum and said first
bleachable dye is present in an amount that provides an optical
density of at least 0.3 in the visible region of the spectrum.
6. The article of claim 2 wherein said non-visible dye absorbs
strongly in the ultraviolet region of the spectrum and said first
bleachable dye is present in an amount that provides an optical
density of at least 0.3 in the visible region of the spectrum.
7. The article of claim 3 wherein said non-visible dye absorbs
strongly in the ultraviolet region of the spectrum and said first
bleachable dye is present in an amount that provides an optical
density of at least 0.3 in the visible region of the spectrum.
8. The article of claim 4 wherein said non-visible dye absorbs
strongly in the ultraviolet region of the spectrum and said first
bleachable dye is present in an amount that provides an optical
density of at least 0.3 in the visible region of the spectrum.
9. A process comprising exposing a desensitizable and imageable
article having at least one layer comprising a
tetra(hydrocarbyl)borate, a first bleachable dye, and a second
bleachable dye present in a molar ratio of at least 0.8/1.0 with
respect to said borate and said first bleachable dye providing an
optical density to said sheet, and having a spectral absorption
curve different from the said second bleachable dye to an imagewise
distribution of radiation to bleach said first bleachable dye in an
imagewise fashion and then generally exposing said article to
radiation to bleach said second bleachable dye.
10. The process of claim 9 wherein said exposing to bleach said
second bleach dye desensitizes the majority of the borate remaining
in said article after the imagewise exposure.
11. The process of claim 9 wherein said second bleachable dye is a
substantially non-visible dye absorbing in the infrared or
ultraviolet regions of the spectrum.
12. The process of claim 10 wherein said second bleachable dye is a
substantially non-visible dye absorbing in the infrared or
ultraviolet regions of the spectrum.
13. The process of claim 9 wherein said tetra(hydrocarbyl)borate is
a tetra(aliphatic)borate.
14. The process of claim 10 wherein said tetra(aliphatic)borate is
a tetra(alkyl)borate.
15. The process of claim 12 wherein said tetra(hydrocarbyl)borate
is a tetra(aliphatic)borate.
16. The process of claim 15 wherein said tetra(aliphatic)borate is
a tetra(alkyl)borate.
Description
FIELD OF THE INVENTION
This invention relates to imaging processes and in particular to
dye bleaching image forming systems. A light sensitive system
comprising a dye and a tetra(hydrocarbyl)borate is constructed so
as to be rendered light-insensitive, i.e., fixed, after
development.
BACKGROUND OF THE INVENTION
There exists a vast array of imaging systems having a multitude of
various constructions and compositions. Amongst the more widely
used systems are silver halide light sensitive systems (including
black and white and color photography, dry silver
photothermography, instant photography, and diffusion transfer
systems, amongst others), photopolymeric systems (including
planographic and relief printing plates, photoresist etching
systems, and imaging transfer systems), diazonium color coupling
systems, and others. Each system has its own properties
attributable to the phenomenon which forms the basis of the imaging
technology. For example, silver halide imaging systems are noted
both for amplification (i.e., image densities which can be
increased by further development without additional imagewise
exposure) due to the catalytic action of silver towards the
reduction of silver ion and for the fact that light sensitivity may
be stopped after development by washing away the light sensitive
silver halide salt (i.e., fixing). Photopolymeric systems are noted
for image stability and ease of application of the imaging layer.
Diazonium color coupling systems have high image resolution and are
easy to coat onto supporting substrates.
One other type of imaging system which has received some attention
in recent years uses a salt comprising an aromatic
tetra(hydrocarbyl)borate anion as a dye-bleaching or
solubility-altering photosensitive compound. U.S. Pat. No.
3,567,453 discloses the use of such borate salts (having at least
one aryl substituent on the borate) in photoresist and lithographic
compositions. U.S. Pat. No. 3,754,921 discloses an imaging system
comprising a leucophthalocyanine and "phenylboronate". U.S. Pat.
No. 3,716,366 even indicates that image stabilization might be
achieved by reaction or dissolution and removal of one of the
components (column 5, lines 1-8). British Pat. Nos. 1,370,058;
1,370,059; 1,370,060; and 1,386,269 also disclose dye bleaching
processes using aromatic borates as light sensitive agents. U.S.
Pat. No. 4,307,182 shows a wide range of constructions for
tetra(aliphatic)borate imaging systems.
U.S. Pat. No. 3,716,366 suggests that desensitization may be
effected by reactions with one of the components to form stable
colorless products, and specifically suggests selectively
dissolving out one of the components. No specific reagents or
reaction mechanisms are suggested for the desensitization process,
however.
U.S. Pat. No. 4,343,891 describes a process for fixing
tetra(hydrocarbyl)borates by chemical reaction of the borate.
SUMMARY OF THE INVENTION
It has been found that light sensitive imaging systems having a
tetra(hydrocarbyl)borate as a light sensitive component thereof may
be rendered light insensitive, particularly after imaging has been
effected, by reacting the borate with a non-visible image-forming
dye in reactive association with the borate within the imaging
system. The most generally useful borate containing light sensitive
systems comprise a borate and a dye in reactive association,
usually in a binder. Cationic dyes are particularly useful in such
construction.
DETAILED DESCRIPTION OF THE INVENTION
Borates are variously referred to in the art as borates, boronates,
boronides and by other chemical terms. In the practice of the
present invention borates are strictly defined as
tetra(hydrocarbyl)borates, that is, a compound having four
carbon-to-boron bonds. These compounds may be represented by the
formula: ##STR1## wherein
R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are independently any groups
bonded to the boron from a carbon atom, and
X.sup..sym. is any cation except for H.sup..sym. and other
boron-carbon bond cleaving cations.
The groups R.sup.1, R.sup.2, R.sup.3, and R.sup.4 may be
independently selected from such groups as alkyl, aryl, alkaryl,
allyl, arylalkyl, alkenyl, alkynyl, cyano, heterocyclic rings,
alkyl-heterocyclic rings, etc. Any group bonded to the boron from a
carbon atom is useful. When these substituents are referred to as
groups, i.e., alkyl group versus alkyl, that nomenclature
specifically is defined as allowing for substitution on the alkyl
moiety (e.g., ether or thioether linkages in the alkyl chain,
halogen, cyano, vinyl, acyloxy, or hydroxy substitution, etc.),
remembering that the group must be bonded to the boron from a
carbon atom. Thus, alkoxy and phenoxy would not be included.
Cycloaliphatic groups are included in the definitions, as are
heterocyclic groups bonded to the boron from a ring carbon atom or
through an alkyl linkage (i.e., alkyl-heterocyclic). It is
preferred that the R groups be selected from aryl (e.g., phenyl or
naphthyl groups), alkyl (e.g., methyl, octyl, octadecyl), alkenyl,
alkynyl, allyl, and aralkyl (e.g., benzyl) groups. Preferably these
groups contain no more than 20 carbon atoms. More preferably they
contain no more than 12 carbon atoms and most preferably no more
than 8 carbon atoms. Cyano is the least preferred aliphatic
group.
The more preferred borates are those having at least three
aliphatic groups bonded to the boron, and the most preferred
borates have four aliphatic groups bonded to the boron.
Any cation may be used in association with the borate except for
cations which break at least one carbon to boron bond on the
borate, e.g., H.sup.+. As a standard test, one could limit the
cations to those which do not break at least one carbon to boron
bond of tetraphenylborate. This can be readily determined by
standard analytical techniques such as gas chromatography, infrared
or mass spectrometry, nuclear magnetic resonance, etc. It is highly
preferred that the cations, if they are metal cations, be less
readily reducible than ferric ions. Readily reducible metal ions
are undesirable as they tend to react with the borate. Organic
cations are preferred. The nature of the cation has not been found
to be critical in the practice of the present invention. The most
significant contribution of the cation is its effects upon
solubility in different solvents or binders. The cations may range
from simple elemental cations such as alkali metal cations (e.g.,
Li.sup.+, Na.sup.+. and K.sup.+) to complex cationic dyes and
quaternary ammonium cations, e.g., such as represented by the
formula: ##STR2## wherein R.sup.5, R.sup.6, R.sup.7, and R.sup.8
are independently selected from aliphatic (e.g., alkyl and
particularly alkyl of 1 to 12 or preferably 1 to 4 carbon atoms),
aryl (e.g., phenyl and naphthyl groups), and aralkyl (e.g., benzyl
groups). For example, tetramethyl, tetraethyl, tetrapropyl,
tetrabutyl and triethylmonomethyl ammonium are particularly useful.
Cations such as phenyltrimethylammonium and benzyltriethylammonium
are also quite satisfactory as are phosphonium and sulfoniums.
Quaternary cations in more complex forms such as N-alkyl
heterocyclic cations such as ##STR3## quaternary dyes and
quaternized groups in polymer chains are useful. The polymers, for
example, could contain repeating groups such as: ##STR4## With the
proper selection of the quaternary ammonium cations, such polymeric
materials could also serve as binders for the system.
The dyes, for example, may be of any color and any chemical class.
These dyes, of course, should not contain groups which would react
with the borate salts without light exposure (e.g., free carboxylic
acid groups, free sulfonic acid groups, or metal ions more readily
than or as readily reducible as ferric ion). Any dye
photobleachable by borates may be used in the practice of the
present invention. Specific classes of dyes useful in the practice
of the present invention include methines, triarylmethanes,
cyanines, ketomethylenes, styryls, xanthenes, azines,
carbocyanines, butadienyls, azomethines, etc. The following are
specific examples of dyes used in the practice of the present
invention: ##STR5## Cationic dyes are the most preferred and when
they have been used, a slight excess of borate anion is desired to
provide complete bleaching.
The cationic dyes may have anions other than borates, such as the
ionic dyes of the formula: ##STR6## wherein
X.sup.- is any anion including, for example, Cl.sup.-, I.sup.-,
Br.sup.- perfluoro(4-ethylcyclohexane)sulfonate (referred to as
PECHS, herein), sulfate, methyl sulfate, methanesulfonate, etc.
R.sup.9 and R.sup.10 are independently H, alkyl or alkoxy
(preferably 1 to 12 carbon atoms and most preferably 1 to 4 carbon
atoms), F, Cl, Br, and I, and
R.sup.11 is H or alkyl, preferably of 1 to 12 and most preferably 1
to 4 carbon atoms, or halogen. Any cationic dye may be useful in
the practice of the present invention, and their listing is merely
cumulative.
Imaging in the light-sensitive systems comprising
tetra(hydrocarbyl)borate, dye and binder is effected by
irradiation. The radiation which is absorbed by the dye-borate
system causes the dye to bleach. A positive-acting imaging process
is thus effected. The use of cationic dyes is believed to cause
spectral absorption of radiation enabling the dyes to react with
the borates. The dyes associated with the borate are not spectral
sensitizers as understood in the photographic silver halide sense
and are not used as sensitizing dyes are used in photographic
imaging systems (the latter are usually in ratios of 1/500 or
1/10,000 of dye to light sensitive agents). The present dyes are
used in proportions of at least 1/10 to about 1/1 in ratio to the
borates. Because the dye-borate system combines the spectrally
sensitive element and the image forming element at a molecular
level, a multiplicity of colored dyes may be used (e.g., cyan,
magenta, and yellow) in the same or different layers or in
dispersed particles or droplets.
The above-described spectral sensitivity relationship between the
dyes and the borates is important to the practice of the present
invention. By incorporating additional dye or dyes in the element,
a light-activated fixing function may be provided to the element.
For example, if an element were constructed which was intended to
provide a blue image only (absorbing the red, yellow, and green
sections of the spectrum), it would ordinarly contain only a blue
dye in a ratio to borate that would not exceed 1:1. If a yellow dye
were also included in the element in a ratio of at least 1:1 with
the borate, the element could readily be desensitized or fixed in
the following manner. The positive-acting imaging film would first
be imagewise exposed (and thereby developed) typically to yellow
light to form the final image. After the image is formed, the film
would be uniformly exposed to blue light to fix the element. The
yellow dye would absorb the blue photons and be at least partially
bleached by the remaining borate, effectively deactivating all of
the borate in the film. After this second exposure, the film would
no longer be light sensitive and would retain the blue positive
image.
Because of the mechanism of the reaction and the order of the
steps, if a second visible dye is used to react with the borate,
all of that second visible dye will not be bleached in the area
where the first visible dye was bleached. This leads to final
images with different colors in the image and background, for there
cannot always be enough borate in one area to bleach both the image
forming dye and the second visible dye. This is not necessarily an
undesirable effect, because with proper choice of the dyes, the
second dye need not interfere with the image information presented
by the first dye, and images with colored backgrounds are quite
useful. Ordinarily in such a system, the total amount of dye
present should be in a ratio of at least 1.1 moles dye1.0 moles of
borate up to a practical maximum of about 2 or 3 moles dye/1.0
moles borate. The moles of dye include the sum of both the image
forming dye and the distinct, differently colored second
(desensitizing) dye. Where the intended use is for visual
presentation, it is preferable to have significant visible contrast
between the dyes so as to provide a distinct image. Combinations
such as cyan/yellow, yellow/cyan, yellow/magenta, cyan/magenta,
green/cyan, green/yellow, etc. are examples of the type of
combinations which would provide significant visible contrast
between the colors of the dyes. The image dye should be present in
sufficient quantity to provide an optical density of at least 0.1,
preferably at least 0.3 or 0.5, and most preferably at least 1.0.
For many uses, the optical density need not be within the visible
regions of the spectrum. Dyes may be used, for example, with
absorption peaks in different regions of the ultraviolet range.
Generally, visual images are preferred on a white or transparent
background. It is therefore necessary to provide a system which
will not be colored in the background. This would be difficult to
do if solely visible dyes were used since the various uses would
differ greatly in the amount of image dye bleached in different
parts of the image and would require almost a predetermined
imagewise distribution of the visible desensitizing dye in order to
react properly with the borate. This problem can be minimized or
completely eliminated by using a dye which absorbs little or no
radiation in the visible region of the spectrum but has absorption
peaks in the near ultraviolet, far ultraviolet, or near infrared,
positions of the spectrum. These regions will be collectively
referred to as the ultraviolet and infrared. By using dyes which do
not absorb strongly in the visible portion of the spectrum,
background images are not a problem; the dyes are only slightly
visible or invisible to begin with. The borate may then be reacted
and deactivated by exposing the element to the particular radiation
which the ultraviolet or infrared absorbing dye absorbs. The borate
then reacts with and bleaches the dye giving another non-visible
light absorbing species and is thereby spent. By exposing the
entire sheet to that radiation after imaging has been performed,
all of the borate will be deactivated.
It is generally preferable to have this non-visible desensitizing
dye present in a molar amount in a ratio of at least 0.8 moles
dye/mole borate. More preferably the desensitizing dye would be
present in a molar ratio of at least 0.9/1.0 dye/borate and most
preferably at least 1.0/1.0. As the dye tends to be invisible, the
upper limit depends only upon the dye's solubility, the structural
requirements of the layer (too much dye may render the layer
physically weak), and the relative invisibility of the dye. Molar
ratios of dye/borate of 10/1, for example, would be possible in
certain circumstances.
When the dye has been termed non-visible, it is intended that this
allows for some absorbance within the visible spectrum, in addition
to its absorption in the infrared and ultraviolet. This is actually
quite common for dyes which strongly absorb in those positions of
the electromagnetic spectrum. Generally the term "non-visible" as
used in the practice of this present invention means that the dye,
as it appears in the element, does not provide an image density of
greater than 0.3 in the visible region of the spectrum. Preferably,
the desensitizing dye, as opposed to the image forming dye would
have an optical density of less than 0.20 and more preferably less
than 0.10 in the visible portions of the spectrum.
The borate should generally be present as at least 0.2% by weight
of the layer and preferably in excess of 0.3%. Smaller percentages
may be preferably with especially thick layers as may be used in
holography.
These and other aspects of the present invention will be shown in
the following examples.
EXAMPLE 1
The following solution was prepared and coated at three (3) mils
wet thickness onto 2 mil polyester sheet:
(1) 5 ml of a 10% solid solution of a
methylacrylate/methylmethacrylate copolymer having a glass
transition temperature of 45.degree. C. in
methylethylketone/toluene (3/1 weight mixture), 30 mg of
tributylphenylboratetetrabutyl ammonium salt, 30 mg of the cyan dye
##STR7## and 60 mg of the ultraviolet radiation absorbing dye
##STR8## The sample was air dried, exposed imagewise to
predominantly red light and then exposed to a hand-held
mercury-vapor ultraviolet lamp for 2 to 3 minutes. Substantial
fixation occurred which was indicated by the stability of the
visible image to white light.
EXAMPLE 2
The following solution was prepared and coated at 3 mil wet
thickness onto 2.5 mil polyester sheet:
(1) 5 mil of a 10% by weight solution of a
methylacrylate/methylmethacrylate copolymer with a glass transition
temperature of 45.degree. C. in methylethylketone/toluene (3:1
weight ratio), 45 mg tetrabutylborate-tetrabutyl ammonium salt, 45
mg of the magenta dye ##STR9## and 90 mg of the same ultraviolet
radiation absorbing dye used in Example 1.
After air drying, the element was exposed imagewise to
predominantly green light, and then was exposed to a hand-held
mercury-vapor ultraviolet lamp for 2 to 3 minutes. Substantial
fixation occurred.
The binders useful in the present invention must be transparent or
at least translucent to the active wavelengths of light. According
to some practices of the present invention, the layers need not be
penetrable by solvents or gases. Binders such as natural resins
(e.g., gelatin, gum arabic, etc.), synthetic resins (e.g.,
polyacrylates, polyvinyl acetals, cellulose esters, polyamides,
polycarbonates, polyolefins, polyurethanes, polyepoxides,
polyoxyalkylenes, polyvinylhalides, polysiloxanes,
polyvinylacetate, polyvinyl alcohol, etc.), and other media may be
used. The binders may be thermoplastic or substantially
crosslinked.
If an imagewise exposure of the desensitizing dye is first made,
with a subsequent general exposure of the element to white light or
light absorbed by the image dye, a negative visible image can be
formed. Care would ordinarily be taken to avoid use in the second
exposure of radiation that would be absorbed by the desensitizing
dye.
It is not intended that the use of terms such as "visible" should
restrict the invention to only those uses in which the images are
examined by the human eye. By suitable choice of the imaging and
densensitizing dyes, a wide variety of exposing radiations may be
used. Furthermore, the use of physical, chemical and biological
detectors of radiation other than human vision make it possible to
use dyes which would be invisible to the human eye.
Normally, it is preferable to ensure that the spectral absorption
band of the image and desensitizing dyes do not overlap at the wave
lengths used respectively for exposure and fixing. However, as long
as considerable difference in absorption exists in those two areas
of the spectrum, usable imaging properties will be present.
* * * * *